Subdivision surface modifier error
You are probably in this situation:



The problem is due to the ngons surrounding the hole: they are not easily processed by the subsurface modifier, so you need to change them into quads.




Enter edit mode
Set mesh select mode to "face" CtrlTab
Select the ngons
Triangulate CtrlT
Make quads AltJ (reselect and redo it as needed)
There is some glitches at the corner
So surround the hole CtrlR
And adjust the position of the surrounding section